Prior to the present invention, various types of superplastic forming equipment and processes have been developed for shaping blanks of metallic sheet material into a wide range of items. The forming dies of such equipment and processes are generally mounted in presses that are capable of maintaining elevated temperatures in the dies and metal sheet material necessary for superplastic forming. More specifically, such temperature elevation enhances the capacity of the metal to tolerate strain-induced deformation without tearing and importantly diminishes the force required for deformation. A time controlled compressed air charge is typically delivered to the forming equipment to apply the force on the heated metal blank to superplastically form the metal on the forming die.
In more specific detail relative to the present invention, superplastic forming involves the employment of a ductile sheet of superplastic metal alloy positioned between dies in a press whose temperature is increased by the heat energy maintained in the press. The heated sheet is stretched by the force of the compressed air into forming cavities or onto forming surfaces of heated forming dies to produce high-quality, lightweight parts such as panels for automotive vehicles. Often such sheets are quite large and components such as trunk lids, engine hoods and these or other large panels can be precisely formed in one piece by such superplastic forming.
Examples of such processes and equipment are found in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Sanders et al. for Superplastic Forming Process and U.S. Pat. No. 5,819,572 issued Oct. 13, 1998 to P. E Krajewski for Lubricating System For Hot Forming, both assigned to the assignee of this invention and both hereby incorporated by reference.
In the patent to Sanders et al. a blank sheet of metal alloy is heated to a superplastic forming temperature and is pulled over and around a forming insert in a die set. Subsequently using differential gas pressure, the sheet is further stretched into conformity with the forming surface of the die insert or other die configuration so that thinning of the formed part is minimized. In the patent to Krajewski, dry lubricant is applied to a metallic sheet which is subsequently heated to predetermined forming temperatures and formed into a part in superplastic forming die equipment. The lubricant initially provides improved forming of the part and subsequently improved release of the formed part from the forming die.
While the above identified patent disclosures provide improvements in super plastic forming they often do not attain new and higher standards for enhanced rates of production of superplastically formed parts.
To improve the rate of production of superplastically formed parts new equipment and processes have been proposed or planned. Copending U.S. patent application Ser. No. 09/950,229 (GP 300636) entitled Plural Sheet Superplastic Forming Euipment and Process by Richard Kleber filed on Sep. 10, 2001, assigned to the assignee of this invention and hereby incorporated by reference is exemplary. In that application a pair of forming blanks are loaded between heated forming dies and a pressurization wedge is forced from one side edge to a position between the sheets to effect pressure sealing therebetween. Pressurized inert gas is fed through passages in the pressurization wedge to the interface of the heated sheets to effect the simultaneous superplastic forming of parts from the two sheets by displacing them onto the profiles of the opposing dies.
In contrast to the prior art, the present invention increases superplastic forming production rates by providing new and improved constructions and methods for the simultaneous formation of at least two sheets of superplastic sheet metal into two separate parts from the same deformation force. Moreover and in further contrast to the disclosure in the above referenced copending patent application, the present invention provides for the employment of a frame-like, pressure-distributing mid plate sandwiched between upper and lower sheets or blanks of superplastically deformable metals. This sandwiched and flattened arrangement of blanks and mid plate is placed between upper and lower die halves mounted in a press that raises the heat energy level of the blanks to a range sufficient to optimize their subsequent plastic deformations.
The dies are subsequently closed to effect peripheral gas tight sealing between the mid plate and the upper and lower sheets. A gas delivery and sheet piercing nozzle carried by one of the dies penetrates one of the blank sheets and operatively seats into a vertical bore or socket formed in one of the sides of the mid plate. This socket communicates with a horizontally-extending, gas-distributing passage provided in at least one side of the mid plate that leads to a centralized gas chamber or space defined by the surrounding sides of the mid plate and the blank sheet arrangement mounted on opposite sides of the mid plate. The forces applied by the expanding pressurized gas such as air, delivered via the nozzle and gas distribution passages into the gas chamber simultaneously effects the displacement of the sheets in opposite directions onto the opposing forming surfaces of the two forming dies. This results in the simultaneous superplastic forming of separate and independent parts or the forming of two mating parts with matching interfaces.
The equipment of this invention provides improved superplastic forming and improved production rates of super plastically formed parts. This invention importantly meets higher standards for quantity production of high quality parts superplastically formed from metallic sheets operatively mounted in hot forming dies particularly using a press and operating at elevated temperatures.
It is a feature, object and advantage of this invention to provide new and improved equipment and methods to produce superplastically formed parts in which a common pressure is introduced to an inner chamber formed between blank sheets peripherally sealed with respect to one another and with upper and lower part forming dies. A pressurized gas is introduced via a gas delivery and sheet piercing nozzle carried by one of the dies and a connecting passage way to the inner chamber provided by a mid plate supporting and separating the blank sheets between the forming dies. The force of this gas displaces the sheets away from one another onto profiling structure of the dies to simultaneously form discrete parts reflective of the upper and lower profiled forming surfaces.
Another feature object and advantage of the present invention is to provide a new and improved die with a gas delivery and sheet piercing nozzle and a cooperating part separating and gas pressure distributing mid plate for superplastic forming. This augments forming of multiple and separate parts from pairs of metallic blank sheets seated on opposite sides of the mid plate and sealed between upper and lower forming dies.
In a preferred form of the invention a frame-like mid plate having flattened upper and lower contact sides with peripheral fluid seals is sandwiched between upper and lower sheets of metal to be superplastically formed. This sandwiched arrangement is operatively placed between heated forming dies in a press that is subsequently closed and pressurized gas from a nozzle carried by a die which pierces a sheet is injected into a pressure chamber formed within the confines of the frame and the upper and lower sheets mounted thereon. The sheets heated by heat energy transferred from the dies, are displaced in opposite directions by injected gas pressure and superplastically form against the forming surfaces thereof.
With this process and equipment the blank sheets can all be of the same dimensions facilitating handling, forming, and consequently identical pairs of parts can be readily formed with reduced trimming and scrap. The sheets may be of differing dimensions and material depending on specifications.